1. Field of the Invention
The present invention relates to machines for washing paper stock pulp and other free-filtering materials.
2. State of the Art
According to various processes well-known in the paper making industry, paper stock pulp is formed by digesting wood chips in the presence of various chemicals in a heated pressure vessel. After discharge from the pressure vessel, the paper stock pulp must be washed and filtered to separate the wood fibers from the digestion chemicals.
According to a conventional system for washing paper stock pulp the pulp is diluted with water after digestion and then is picked up by a large-diameter rotating cylinder whose surface is formed of a wire mesh screen. A couch roll is positioned to press downward onto the surface of the screen-covered cylinder to express liquid from the stock and thus to form a blanket or mat of dewatered fibers. Such a conventional system further includes an agitation device wherein once-dewatered fibers are repulped by mixing with water. Still further, the system includes additional agitation devices, screen-covered cylinders, and couch rolls to wash the pulp in stages.
According to other processes well-known in the paper-making industry, materials such as waste paper and ground-wood, although not digested with chemicals, must nevertheless be washed. Conventional systems for such washing are also known.
According to still other processes well-known in the paper-making industry paper pulp is bleached by treating the pulp with chemicals such as a solution of chlorine or sodium hydroxide. In other processes chemical solutions are often used to treat the pulp.